An aircraft ejector rack is a device used to carry and release stores such as bombs and missiles from an aircraft in flight. These racks are typically mounted to the undersurfaces of aircraft wings and fuselages and incorporate both release and ejection features. The release features normally include bails or hooks from which stores may be suspended, and the ejection features normally include pneumatically operated thrusters for forcibly ejecting stores away from the aircraft to minimize the possibility of their colliding with the aircraft after release.
A contemporary ejection rack system of the type described above incorporates an onboard pressurization capability, employing a single pressurization system capable of operating multiple release mechanisms and uses air to operate both the store release bails and thrusters. The system also includes a miniature compressor and a gas purification system which filters, dries, and stores ambient air as an energy medium. With the onboard compressor, pressure in the system can be maintained at the desired operating level regardless of system usage or temperature changes in the gas. The use of air eliminates the problems associated with the use of pyrotechnics to generate high pressure gasses, such as periodic cleaning required by the corrosives and moisture generated in such systems, and also eliminates the sealing problems commonly found in hydraulically operated ejector racks. An example of such a state-of-the-art pneumatically operated ejector rack system is seen in U.S. Pat. No. 5,583,312, which is incorporated herein by reference.
It is common in the above-described prior art ejector rack systems to release a store by simultaneously pressurizing the hook release mechanism and the thrusters. The problem with such simultaneous pressurization is that it results in significant forces being applied to the store before the hook is fully opened, resulting in the transfer of those forces to the release mechanism. If those forces are sufficiently high, the release mechanism may jam or stall and the store may not be released. Secondly, the force required to open the hook may result in the excessive consumption of energy in the gas so that insufficient energy is available to power the thruster. One solution to this problem is proposed in U.S. Pat. No. 6,347,768, incorporated herein by reference, which discloses a fluid actuator for ejector rack systems which stages or sequences the operation of the hook release mechanisms and the thrusters. FIG. 4 of that patent illustrates an actuator including a valve assembly which controls the flow of high pressure gas from an accumulator to the thrusters. The valve is also mechanically connected by a rod and a release ram to a hook release mechanism. The valve includes a cylindrical projection, referred to as a tab, which enters a bore in the valve seat when the valve is in its uppermost or closed position. Upon command, the valve moves downward, engaging the hook release mechanism when the valve is moved downward a predetermined distance. When the hook is fully opened, the tab on the valve head clears the valve seat, permitting high pressure air to pass to the thrusters. The problem encountered with this device is that because the tab is unsealed in the bore, it permits the leakage of high pressure air through the valve as soon as the primary valve is unseated which results in the loss of energy and the premature pressurization of the thruster.
Accordingly, there is an unmet need in the prior art to provide for an aircraft stores ejector rack having a fluid actuator which pressurizes the hook release mechanism prior to the pressurization of the thrusters, thus avoiding the loss of fluid energy and jamming of the hook release mechanism.
Moreover, there is a further unmet need in the prior art to provide for such a fluid actuator including a staged valve assembly connected to the hook release mechanism which permits passage of high pressure gas to the thruster only after the hook release mechanism has moved the hook to the open position.